1. Field of the Invention
The present invention relates to an image capture device, an anomalous oblique incident light detection method, and a recording medium, and particularly, relates to a method for detecting an anomalous oblique incident light such as a flare light.
2. Description of the Related Art
If an intense light is incident on a lens when a subject image is imaged by an image capture device such as a digital camera, a light reflected on a surface of an imaging lens or macro lens is complexly reflected inside the lens or inside the camera such that a light travelling at an unintended angle is sometimes received by an image pickup device. An anomalous oblique incident light incident on the image pickup device at an unintended angle in this way gives rise to a phenomenon such as a so-called ghost, flare or the like to degrade a captured image.
In a case, among others, where the angle of the anomalous oblique incident light is large, at least a part of the anomalous oblique incident light is incident on a photodiode adjacent to a color filter through which the light passes. In the case like this where a color filter through which an anomalous oblique incident light passes and a photodiode actually receiving that light do not completely coincide with each other, this anomalous oblique incident light causes significantly a so-called color mixing phenomenon to lead to color reproducibility degradation of the captured image. Particularly, a long wavelength component (e.g., red light component) gives rise to the color mixing phenomenon between adjacent pixels.
For example, if aperture is F2.8 in image-capturing, it is sufficient that an incident light of about ±10 is incident on each pixel, but there is a concern that an internal reflection in the lens, a reflection between a glass lid and the image pickup device or the like causes an anomalous oblique light to be incident on each pixel at an unexpected angle.
Especially, in recent years, employment of a backside illumination type image pickup device has caused increase of a possible angle of incidence in each pixel of the image pickup device, which has further increased possibility of an anomalous oblique incident light being illuminated on each pixel from an unintended angle.
Since it is characterized that the longer the wavelength component, the deeper the anomalous oblique incident light penetrates into an inside of silicon, the anomalous oblique incident light in a band of longer wavelength has lager effect on surrounding pixels. Therefore, in a case where an RGB color filter is used in the image pickup device, an effect from color mixture caused by the anomalous oblique incident light passing through an R filter is liable to be distinguished in output data of a pixel arranged adjacent to a pixel as the R filter.
For example, PTL 1 (Japanese Patent Application Laid-Open No. 2001-145117) discloses, as a method for reducing such effects from the anomalous oblique incident light, an electronic image pickup device capable of reproducing an image having a color flare reduced. According to this electronic image pickup device, an area is detected which has a pixel of luminance difference exceeding a certain level among the certain number of adjacent pixels (e.g., six pixels) where the color flare is distinguished.
PTL 2 (Japanese Patent Application Laid-Open No. 2005-136852) discloses an image processing apparatus that corrects image components corresponding to a non-image-forming light in image data. According to this image processing apparatus, a flare image corresponding to an unnecessary diffraction light is silhouetted against a background image on the basis of a difference between an average luminance value of an adjacent pixel group and a luminance value of a notice pixel group, the adjacent pixel group corresponding to a diameter of the flare image depending on a diffraction order.